The present invention is generally directed to monitoring whether a trailer portion of a tractor/trailer rig is connected to the tractor portion. More particularly, the invention is directed to a system for sensing whether an electrical umbilical cable or tether is connected or disconnected between the tractor portion and the trailer portion.
Hundreds of thousands of tractor/trailer rigs travel the roadways hauling cargo from one location to another. Often, when a tractor/trailer rig has reached its destination, the trailer is disconnected from the tractor for unloading. The tractor may then be connected to another trailer for transport to another destination. To keep track of the status of individual trailers, monitoring systems have been developed which attach to the trailer for sensing various conditions of the trailer and for transmitting signals to a central location to indicate the condition of the trailer.
One of the conditions typically monitored by such systems is whether or not the trailer is attached to the tractor. Previous systems developed to monitor the connect/disconnect status of a trailer have been unnecessarily complicated, difficult to implement, and/or unreliable.
What is needed, therefore, is a simple and reliable system for detecting the connect/disconnect status of the tractor and trailer portions of a tractor/trailer rig, and for transmitting a signal that is indicative of the connect/disconnect status.
The foregoing and other needs are met by an apparatus for detecting whether an electrical connection exists between a first vehicle portion and a second vehicle portion of a multi-portion vehicle. The apparatus includes a first chassis electrical ground in the first vehicle portion and a second vehicle chassis ground in the second vehicle portion. A first electrical conductor, such as a wire in an umbilical cable, is coupled to the first chassis electrical ground, preferably through a first appliance circuit, such as a turn indicator light circuit in the first vehicle portion. A second electrical conductor, such as a contact in a connector on the second vehicle portion which mates with the umbilical cable, is operable to electrically connect to and disconnect from the first electrical conductor. The apparatus also includes a detection circuit for providing an indication based upon whether an electrical connection exists between the first electrical conductor and the second electrical conductor. The detection circuit includes a diode having an anode which is electrically connected to the second electrical conductor, where the anode has an anode voltage thereon. The diode has a cathode which is electrically coupled to the second vehicle chassis ground, preferably through a second appliance circuit, such as a turn indicator light circuit in the second vehicle portion. The detection circuit also includes a biasing-current source for providing a forward biasing current to the anode of the diode. The detection circuit further includes a comparison circuit for providing an output signal indicative of a voltage level at the anode of the diode, where the voltage level at the anode of the diode is dependent at least in part upon whether an electrical connection exists between the first electrical conductor and the second electrical conductor.
Some preferred embodiments of the invention include a first appliance circuit disposed in the first vehicle portion. The first appliance circuit includes, in series, a first voltage source for supplying a first voltage, a switching device connected to the first voltage source, a first vehicle appliance connected to the switching device, and the first vehicle chassis ground connected to the first vehicle appliance. In these preferred embodiments, the first electrical conductor is connected to the first appliance circuit between the switching device and the first vehicle appliance.
Some embodiments include a first reference voltage source for providing a first reference voltage, and a second reference voltage source for providing a second reference voltage having an amplitude greater than the first reference voltage. In these embodiments, the comparison circuit receives the anode voltage, the first reference voltage, and the second reference voltage, provides the output signal having a first signal indication when the amplitude of the anode voltage is less than the first reference voltage, and provides the output signal having a second signal indication when the amplitude of the anode voltage is between the amplitudes of the first and second reference voltages.
In another aspect, the invention provides a method for detecting whether an electrical connection exists between a first vehicle portion and a second vehicle portion of a multi-portion vehicle. The method includes the steps of sensing a node voltage level on an electrical node coupled to an appliance circuit in the second vehicle portion, and generating an indication signal indicative of a relationship between the node voltage level, a first reference voltage level, and a second reference voltage level. According to the preferred embodiment of the method, the indication signal indicates no electrical connection between the first and second vehicle portions when the node voltage level is greater than the first reference voltage level and less than the second reference voltage level. The indication signal preferably indicates the existence of an electrical connection between the first and second vehicle portions when the node voltage level is less than the first reference voltage level or greater than the second reference voltage level.